The content of the COPEPOD plankton database is updated on a monthly-to-quarterly basis.
Every two years a printed NOAA technical memorandum is created to summarize the full data content, as well as the latest protocols for quality control and data product synthesis (i.e., new gridded fields, compilations, etc.).
This allows users to cite a printed reference or a web site (depending on preference and/or the requirements of their intended publication or works).

The most recent printed NOAA technical memorandum (NMFS-F/ST-34, aka "COPEPOD-2007") is available as
an electronic PDF file (here) .
The database can be cited as follows:

O'Brien, T.D. 2007.COPEPOD: The Global Plankton Database.

A review of the 2007 database contents and new quality control methodology.U.S. Dep. Commerce, NOAA Tech. Memo. NMFS-F/ST-34, 28p.